School children primarily get cutaneous warts caused by infection with human papillomavirus (HPV) from family members and classmates, a Dutch study showed.

Action Points

School children primarily get cutaneous warts caused by infection with human papillomavirus (HPV) from family members and classmates.

Point out that neither an individual's preexisting wart status nor the use of public swimming pools were associated with the risk of developing warts in the current study.

School children primarily get cutaneous warts caused by infection with human papillomavirus (HPV) from family members and classmates, a Dutch study showed.

After accounting for other factors, having a family member with warts was associated with double the risk of a child developing warts (hazard ratio 2.08, 95% CI 1.52 to 2.86), according to Sjoerd Bruggink, MD, of Leiden University Medical Center in the Netherlands, and colleagues.

The prevalence of warts within a class also was associated with a greater risk of developing warts (HR 1.20 for every 10% increase in prevalence, 95% CI 1.03 to 1.41), the researchers reported online in Pediatrics.

Even though existing recommendations for combating the spread of warts focus on limiting individual spread of HPV and transmission in public venues, neither an individual's preexisting wart status nor the use of public swimming pools were associated with the risk of developing warts in the current study.

"Our findings suggest that recommendations should shift toward reducing transmission among families and school classes," the authors wrote. "For example, covering warts at home potentially prevents transmission more effectively than covering warts in the swimming pool."

Bruggink and colleagues conducted a prospective study of children, ages 4 to 12, attending one of three elementary schools in and around Leiden. A trained medical student examined the hands and feet of the children for warts at baseline and after 11 to 18 months of follow-up. Parents completed questionnaires about possible exposures.

The study included 1,099 children at baseline; 91% completed a follow-up examination. The median age of those who had a follow-up exam was 7. One-third had warts at baseline.

The children developed warts at a rate of 29 per 100 person-years at risk during follow-up (95% CI 26 to 32). That rate is higher than previously observed in studies based on family physician registries (three to five per 100 children), which "is explained by the fact that many warts are unnoticed by children and parents, and many warts are treated with over-the-counter medication, or not treated at all," the authors wrote.

In addition to having family members with warts and having a higher prevalence of warts in class, having white skin was associated with a greater risk of developing warts during follow-up (HR 2.3, 95% CI 1.3 to 3.9).

The researchers classified types of exposures into four categories -- individual, family, school, and public. Each additional type of exposure was associated with an increased risk of developing warts in a dose-response fashion (HR 3.5, 95% CI 2.9 to 4.2).

Although expected to be the main risk factor, according to Bruggink and colleagues, a personal history of warts was not independently associated with the development of warts.

"This could be explained by the fact that, besides HPV exposure, immunogenicity and susceptibility of the host to specific HPV type are important to develop warts," they wrote. "In other words, the immune system of the child with warts could already be triggered and might therefore be more effective against the specific HPV type the child is exposed to."

The findings were similar in the subgroups of children with plantar warts and those without warts at baseline.

The authors acknowledged that their protocol might have missed warts on parts of the body other than the hands and feet and did not consider certain difficult-to-measure risk factors related to HPV exposure, including the sharing of personal objects and close contact with children with warts during specific activities.

The study was supported by the Netherlands Organization of Health Research and Development, Fund Common Diseases.

The authors reported no conflicts of interest.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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